NASA postponed the launch of the space shuttle Endeavour today because of cloudy skies over the Kennedy Space Center in Florida.

Low clouds descended over the launch pad about two hours before the planned 0939 GMT liftoff, violating safety rules for the flight.

"We just were not comfortable with launching the space shuttle tonight," said launch director Mike Leinbach. "It's just too dynamic."

Endeavour and its six astronauts had been scheduled to take off before daybreak on a 13-day mission to install two new modules on the International Space Station. The next launch opportunity would be tomorrow at 0914 GMT.